Unambiguous optical characterization of nanocolloidal gold films

Abstract

The thin island film theory developed by Bedeaux and Vlieger [Optical Properties of Surface (Imperial College Press (2002)], is used to unambiguously analyze spectroscopic ellipsometry spectra of thin layers of nanocolloidal gold particles on silicon substrates covered by a natural oxide layer, for coverages up to 35%. Due to the absence of isotropy in three dimensions, standard effective medium theories cannot be applied. Image dipole effects as well as the lateral distribution of colloids have to be taken into account as described by Bedeaux and Vlieger. Additonally we show that an effective image dipole has to be taken into account if colloidal particles are adsorbed on a substrate that is terminated with a thin SiO2 layer with a thickness that is smaller than the radius of the gold nanoparticles (a = 6.7 nm). The natural oxide layer on our Si subtrates is only a fraction of this.